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[Tom958]

Different highway agencies have different design philosophies and policies. When those policies are more expensive than those followed by other states, who covered/covers the extra expense? The Feds, the states, or a bit of each? I'm thinking primarily of median width and treatment during the heyday of Interstate construction, but other items, such as some aspects of bridge design, may qualify as well.

This is a historic and regulatory question, not a debate over highway design features.

 A while back we had a discussion about who paid for Texas' seemingly-ubiquitous frontage roads that I hoped would shed some light on the question I'm asking today. However, it turned out that frontage roads were generally cheaper than purchasing access rights to affected properties and were thus just as deserving of federal funding as right-of-way acquisition was, so... no help there, though the question could arise over the conversion of basic frontage roads to sophisticated one-way feeder roads.

I want to offer another IMO fascinating example: When Idaho built its first Interstates, they went for median widths of about 75 feet instead of the sixtyish feet of most other states. Additionally, like a few other states, Idaho seems to have decided that there was a fairly short advisable upper limit on the length of precast concrete bridge spans. Rather than settling for a narrower median width or using steel or cast-in-place concrete for longer bridge spans, Idaho added an extra span over the median. Of course, in addition to being more expensive that the obvious options, it places two of the bents much closer to the roadway, creating a collision hazard. This isn't a one-off. Well over half of Idaho's Interstates are like this. Did the FHWA sign off on full funding for this, or did sparsely-populated Idaho cough up the bucks itself?

Enquiring minds want to know. This one does, anyway.

[Rothman]

Each state receives an apportionment of federal funds from FHWA.  As long as FHWA determines that submitted projects are eligible for federal funding, the premium for projects that have their own special specs would be borne by the larger amount of federal funds needed.

Of course, for projects not federal-aid eligible, the States can just pony up 100% state funding for the project and absorb any higher costs in their annual budget.

[Dirt Roads]

I want to offer another IMO fascinating example: When Idaho built its first Interstates, they went for median widths of about 75 feet instead of the sixtyish feet of most other states. Additionally, like a few other states, Idaho seems to have decided that there was a fairly short advisable upper limit on the length of precast concrete bridge spans. Rather than settling for a narrower median width or using steel or cast-in-place concrete for longer bridge spans, Idaho added an extra span over the median. Of course, in addition to being more expensive that the obvious options, it places two of the bents much closer to the roadway, creating a collision hazard.

I'm not qualified to do the structural stuff here, but it seems intuitive to me that this bridge design would be less expensive than the comparable two-span structure.  Having done many of these types of cost analyses, I thought that I would play around with the numbers.

I was able to find current IDT standards for stringer lengths versus girder heights.  The existing stringers appear to 50 feet long (the short ones are only 30 feet long).  Assuming this bridge is perpendicular to I-84 (kinda) and also straight (it's not), you end up with a total bridge length of about 210 feet (it's close enough).  These short span lengths only require four stringers (there are five here, placing one beneath each parapet wall).  For the alternative, I knocked off about 15 feet in the median and assumed two long spans.  That results in a bridge length rounded up to 190 feet, which gives us stringer lengths of 95 feet (non-standard, but cheaper than 100-foot standard stringers for fair comparison purposes).  The extra length in girders raises us up to the next structure strength (taller girder web) and also decreases the minimum spacing of stringers (adding one more stringer for each span).  I couldn't find costs for concrete girders in Idaho, but I've got a couple of common resources up my sleeve (doing a comparison here, so the actual cost of concrete doesn't make any difference).  For sake of this comparison, I assumed (perhaps improperly) that the resultant single column structure in the middle would cost roughly the same as the existing four sets of smaller column structures.

Rounding down, it looks like your alternative would be just shy of 17% more expensive than this design just in girder costs.  In addition, there would need to be more frequent placement of diaphragms between the girders, plus the entire overpass would need to be raised (about a foot) with relative incremental costs in fill and piling lengths beneath the abutments.

All that being said, the existing layout would be less than 1% cheaper than your proposed arrangement if constructed today.  I've got a strong suspicion that this was a cookie cutter design that IDT had already paid for (somewhere other than an Interstate highway application) and simply reused, knowing that nobody (errh, cost estimators) could question the cost savings. 

By the way, the stringer designs used here appear to be more expensive than what the current IDT standards require for this type of bridge layout.  For instance, there shouldn't be any need for diaphragms between the stringers (but they are using one in the middle between each of the 50-footers).  IDT actually recommends a newer stringer design that reduces the costs even more than what I was assuming from their data sheets.  If I used the newer standards, I suspect that there would be a much greater differential in the costs.

[Tom958]

Each state receives an apportionment of federal funds from FHWA.  As long as FHWA determines that submitted projects are eligible for federal funding, the premium for projects that have their own special specs would be borne by the larger amount of federal funds needed.

Of course, for projects not federal-aid eligible, the States can just pony up 100% state funding for the project and absorb any higher costs in their annual budget.

Thanks. I guess I could've surmised that, but I didn't. So... I'm in Georgia, casting an envious eye on the luxuriously wide medians and aesthetically superior bridge designs found in Tennessee. By and large, Tennessee's Interstates seem more lavish than those of any of its neighboring states. So, basically, Tennessee looked at its likely apportionment of federal funds over the coming years and decided that they could afford to spend quite a bit more on these highways than they absolutely had to. Standards inflation is a thing and many states' Interstates were more lavish toward the end of the original Interstate era, but Tennessee really took it up a notch or two.

[Tom958]

I'm not qualified to do the structural stuff here, but it seems intuitive to me that this bridge design would be less expensive than the comparable two-span structure.  Having done many of these types of cost analyses, I thought that I would play around with the numbers.

Interesting analysis, but I have to say right off that the fair comparison would've been five spans versus four, not two, or 3-75-75-30, not 95-95. That's what most other agencies were doing. If two spans were comparable in cost to four (or a modest amount more, considering the safety benefit of not having end bents), that would've been the default practice. I mentioned that Idaho added an extra span, not three.

Come to think of it, though, many of the pre-Interstate bridges on I-85 between Greensboro and the I-40 split had five spans despite the narrow median, so the early North Carolinians must've come to the same conclusion that you did.

Tangential to the topic, I mentioned in my survey of bridge design practice in Idaho that Idaho went directly from five-span Interstate bridges to two, without an intermediate four-span phase (excepting, of course, bridges on severe skew angles), which I found rather striking. Of course, doing this required going to steel or cast-in-place construction rather than precast.

[Dirt Roads]

I'm not qualified to do the structural stuff here, but it seems intuitive to me that this bridge design would be less expensive than the comparable two-span structure.  Having done many of these types of cost analyses, I thought that I would play around with the numbers.

Interesting analysis, but I have to say right off that the fair comparison would've been five spans versus four, not two, or 3-75-75-30, not 95-95. That's what most other agencies were doing. If two spans were comparable in cost to four (or a modest amount more, considering the safety benefit of not having end bents), that would've been the default practice. I mentioned that Idaho added an extra span, not three.

Assuming that the older stringers needed to go up one size when going from 50-foot lengths to 75-foot lengths, the cost of stringers for 30'-75'-75'-30' spans would be only a little over 5% more than existing design, plus the additional cost of the complex hammerheads that transition from the thicker beams to the narrower ones.  Somewhere recently in another thread, we had an example of a similar type of complex pier hammerhead.

We could simplify that hammerhead design by using the same stringer size for the short 30-footers.  That bumps the cost of stringers up a little over 7% over the existing design.

To be fair, the design standards I was using does not require a larger size stringer when going from 50-foot lengths to 75-foot lengths.  Because the lengths and required numbers of stringers per span didn't change from those scenarios (as compared to the original), the cost of 30'-75'-75'-30' alternative would be roughly the same as the 30'-50'-50'-50'-30' existing.

So I'm going out on a limb here and suppose that the 50-foot maximum span didn't require a full blown bridge redesign (typically 10% to 12% additive to the construction cost), but rather an application engineering effort (perhaps as low as 6% to 8%).  That reduces the whole bridge about 4% (way more than the 1% impact that these stringers plus 12-inch increased height would have).  There's also a strong likelihood that way more contractors in Idaho back in the 1960s could compete on hanging 50-foot stringers than 75-foot stringers, driving down construction prices (same could probably be said for Central Carolina back in those days). 

[Tom958]

Rounding down, it looks like your alternative...

It's not MY alternative. It's the alternative of a large majority of highway agencies in the US. Do correct me if I'm wrong, but I don't believe there's any other agency that adopted five-span Interstate bridges over 75-foot medians as policy, certainly not on the scale that Idaho did (that is, with near ubiquity up until 1968, best I can tell). 

I know you'll contradict anything I say on this, so I'm gonna ask you one question: If Idaho's policies were so wonderful, why didn't pretty much everyone else follow them?

[Dirt Roads]

Rounding down, it looks like your alternative...

It's not MY alternative. It's the alternative of a large majority of highway agencies in the US. Do correct me if I'm wrong, but I don't believe there's any other agency that adopted five-span Interstate bridges over 75-foot medians as policy, certainly not on the scale that Idaho did (that is, with near ubiquity up until 1968, best I can tell). 

I know you'll contradict anything I say on this, so I'm gonna ask you one question: If Idaho's policies were so wonderful, why didn't pretty much everyone else follow them?

First off, I'm not trying to argue [for or against] your original premise that some states [built their portion of Interstate system] in a manner that was more expensive than other states.  I'm like you, I'm looking at the Idaho bridges and wondering why they would construct a bridge that would prohibit widening the roadway (and as you mentioned, adding the safety issues related to sticking the columns smack dab up against the running lanes).  It's just that those bridges look like they are approaching the least expensive way to span that much territory.

I know you'll contradict anything I say on this, so I'm gonna ask you one question: If Idaho's policies were so wonderful, why didn't pretty much everyone else follow them?

Now to your question.  I think that you already answered this one, but some of the other readers can chime in:

When Idaho built its first Interstates, they went for median widths of about 75 feet instead of the sixtyish feet of most other states.

My only argument here is that if you don't have so much territory to span with overpasses, you don't immediately look for the absolute cheapest bridge design.  By the way, I think that most states that have some of these extra-wide medians actually put fill in the median so as to construct a span over each set of Interstate lanes.  (Which still might be more expensive than Idaho's bridge arrangement).

[Bitmapped]

Rounding down, it looks like your alternative...

It's not MY alternative. It's the alternative of a large majority of highway agencies in the US. Do correct me if I'm wrong, but I don't believe there's any other agency that adopted five-span Interstate bridges over 75-foot medians as policy, certainly not on the scale that Idaho did (that is, with near ubiquity up until 1968, best I can tell). 

I know you'll contradict anything I say on this, so I'm gonna ask you one question: If Idaho's policies were so wonderful, why didn't pretty much everyone else follow them?

I-79 and I-80 in northwestern Pennsylvania were built with ~75 foot medians. They almost universally have 5-span bridges, generally with concrete beams. The same goes for I-81 through the Shendoah Valley in Virginia - largely ~75 foot median and 5-span concrete beam bridges. These areas are relatively flat with easy terrain to build in; in areas with rougher terrain, the DOTs opted for a narrower median footprint with 4-span bridges.

I assume that a lot of the design on bridge spans is tied to which material the DOT preferred and median width.

[J N Winkler]

Different highway agencies have different design philosophies and policies. When those policies are more expensive than those followed by other states, who covered/covers the extra expense? The Feds, the states, or a bit of each? I'm thinking primarily of median width and treatment during the heyday of Interstate construction, but other items, such as some aspects of bridge design, may qualify as well.

Many years ago, while at the Bancroft Library in Berkeley, I ran across a report the California Division of Highways (Caltrans' predecessor agency) compiled in the mid-1960's, presumably in response to a legislative request, on the impact of the Interstate highways to the state's overall construction program.  It mentions that Division of Highway engineers had to deal with federal counterparts trying to nickel and dime various features (such as guardrail) that were then provided on a more generous basis in California.  However, many of these were eventually approved for federal cost-sharing, as a result of "sales pressure" (the report's exact phrase) from the Division engineers.

I don't receive the impression those types of conversations occur anymore.  Rothman describes my sense of the process as it currently exists:  as long as the feature belongs in a fundable category, the feds usually won't sweat the details.  The stylized fact is that state FHWA offices exist on a spectrum of capture by the DOTs they nominally supervise.

[Tom958]

...I'm like you, I'm looking at the Idaho bridges and wondering why they would construct a bridge that would prohibit widening the roadway (and as you mentioned, adding the safety issues related to sticking the columns smack dab up against the running lanes).  It's just that those bridges look like they are approaching the least expensive way to span that much territory.

Exactly. Beyond that, it seems like a disproportionate amount of effort to put into snagging another ten or fifteen feet of median width compared to most other states. Below, Bitmapped helpfully pointed out that significant sections of I-79 and I-80 in Pennsylvania seemed to be similar. I checked, though, and the medians there are more like 84 feet, which strikes me as a more worthy reason to add a span to a bunch of bridges. 75 feet seems hardly worth the effort.

I usually try to remain agnostic about such things, but I really think that what Idaho did was a mistake.

Having said all of this, I must admit that what happened in Idaho isn't a very good example of the kind of extravagance that'd cause a reasonable person to wonder who's paying the bill, compared to Tennessee's crazy-wide medians and (to me) delightfully diverse bridge designs.  I threw my own thread off topic in the OP. 

My only argument here is that if you don't have so much territory to span with overpasses, you don't immediately look for the absolute cheapest bridge design.

Missouri raises its hand.     But that's a different subject.

Closer to the topic, a few of the Idaho five-span bridges are built with precast voided slab panels, which I surmise are much more length-limited than other materials. 

[pderocco]

It's Idaho. By the time those rural roads need widening, we'll all have the flying cars we've been promised for decades.

[Tom958]

I-79 and I-80 in northwestern Pennsylvania were built with ~75 foot medians. They almost universally have 5-span bridges, generally with concrete beams.

Thanks! Checking very quickly, it's actually an 84-foot median on the westernmost 51 miles of I-80 and 58 miles of I-79 (that's north of Porterville-- it's more variable south of there, with more wider sections but a good bit of 60 foot, too).

Of course, 84 feet is a more significant addition to the common 60 feet that the 75ish seen in Idaho, and the bridges aren't especially cheap-looking. These factors make it a better illustration of my point than what was done in Idaho. 

The same goes for I-81 through the Shenandoah Valley in Virginia - largely ~75 foot median and 5-span concrete beam bridges. These areas are relatively flat with easy terrain to build in; in areas with rougher terrain, the DOTs opted for a narrower median footprint with 4-span bridges.

I couldn't find many stretches with a consistent 75ish width, or any other consistent width, for that matter, except minimal ones. Virginia seems to be fond of building truly independently aligned roadways, which is a whole 'nother thing. 

I assume that a lot of the design on bridge spans is tied to which material the DOT preferred and median width.

Exactly. My question is how the feds treated and treat such significant deviations from more-conservative prevailing policies. 

[Tom958]

Many years ago, while at the Bancroft Library in Berkeley, I ran across a report the California Division of Highways (Caltrans' predecessor agency) compiled in the mid-1960's, presumably in response to a legislative request, on the impact of the Interstate highways to the state's overall construction program.  It mentions that Division of Highway engineers had to deal with federal counterparts trying to nickel and dime various features (such as guardrail) that were then provided on a more generous basis in California.  However, many of these were eventually approved for federal cost-sharing, as a result of "sales pressure" (the report's exact phrase) from the Division engineers.

I  vaguely recall hearing about such things myself. Thing is, it's hard for me to reconcile nickel-and-diming minor items like guardrail provision with signing off on 150-200-foot medians and such.

I don't receive the impression those types of conversations occur anymore.  Rothman describes my sense of the process as it currently exists:  as long as the feature belongs in a fundable category, the feds usually won't sweat the details.  The stylized fact is that state FHWA offices exist on a spectrum of capture by the DOTs they nominally supervise.

Ha, yeah. Back in 1994 and continuing into the early oughts, I came into fairly close contact with the Georgia office of FHWA. I had surmised, correctly, that GDOT intended to do something that the feds emphatically shouldn't sign off on, at least not without a great deal more planning and fiscal scrutiny. The head guy told me that the Georgia office saw its role as making sure that GDOT got its money expeditiously, which I found infuriating.

What GDOT wanted to do was grossly unrealistic and never even came close to full fruition, but tens of millions of dollars were wasted on pursuing it anyway, waste that FHWA could and should have prevented or at least resisted. During the Atlanta air quality conformity kerfuffle of that time, the head guy at the Georgia office changed his outlook on the air quality-relevant planning issues, but they never got a handle on the fiscal stuff, if they even tried. I will forever be resentful of it. 

[D-Dey65]

I want to offer another IMO fascinating example: When Idaho built its first Interstates, they went for median widths of about 75 feet instead of the sixtyish feet of most other states. Additionally, like a few other states, Idaho seems to have decided that there was a fairly short advisable upper limit on the length of precast concrete bridge spans. Rather than settling for a narrower median width or using steel or cast-in-place concrete for longer bridge spans, Idaho added an extra span over the median. Of course, in addition to being more expensive that the obvious options, it places two of the bents much closer to the roadway, creating a collision hazard. This isn't a one-off. Well over half of Idaho's Interstates are like this. Did the FHWA sign off on full funding for this, or did sparsely-populated Idaho cough up the bucks itself?

The reasons for the third spans vary from state to state. North Carolina has them on I-95 for contra-flow during hurricane evacuations. On the other hand, some are a little sketchier. There's a notable one in my former hometown that was said to be proposed for a railroad line which was never built. Naysayers may look at this and reply, "well that's further proof that Robert Moses was out to destroy the railroads," but I don't think that's the case. The main line of the Long Island Rail Road has been in the same straight line through Medford since 1844. Now we're supposed to believe that there's a good reason to create a jughandle to go under Horse Block Road between the Long Island Expressway just for the hell of it? I don't think so.

[J N Winkler]

I  vaguely recall hearing about such things myself. Thing is, it's hard for me to reconcile nickel-and-diming minor items like guardrail provision with signing off on 150-200-foot medians and such.

Actually, rural land has to be pretty valuable before the cost of acquisition starts to be comparable to construction cost.  Each additional 100 feet in corridor width translates to 13 acres per centerline mile, which is only about $66,000 at the US national average cropland value of $5,050 per acre as of 2022.  In comparison, for estimating purposes Florida DOT now uses a nominal construction cost of $8.2 million per mile of four-lane Interstate with the minimum shoulder widths of four feet on the left and 10 feet on the right.

And even with this disparity, median widths of 200 feet or thereabouts tend to be seen more often in terrain where land values are very low, such as the desert in Arizona.  Most of Kansas' freeway mileage has a median width of 60 feet with average farmland value (as of 2022) of about $3000 per acre.

[Tom958]

Actually, rural land has to be pretty valuable before the cost of acquisition starts to be comparable to construction cost.  Each additional 100 feet in corridor width translates to 13 acres per centerline mile, which is only about $66,000 at the US national average cropland value of $5,050 per acre as of 2022.  In comparison, for estimating purposes Florida DOT now uses a nominal construction cost of $8.2 million per mile of four-lane Interstate with the minimum shoulder widths of four feet on the left and 10 feet on the right.

And even with this disparity, median widths of 200 feet or thereabouts tend to be seen more often in terrain where land values are very low, such as the desert in Arizona.  Most of Kansas' freeway mileage has a median width of 60 feet with average farmland value (as of 2022) of about $3000 per acre.

Ha, I had no idea that rural land was that cheap. Wow. The cost of additional bridgework would surely be more than that. 

[Dirt Roads]

Actually, rural land has to be pretty valuable before the cost of acquisition starts to be comparable to construction cost.  Each additional 100 feet in corridor width translates to 13 acres per centerline mile, which is only about $66,000 at the US national average cropland value of $5,050 per acre as of 2022. 

That number actually seems a bit high.  Do you know if this is property values or land acquisition costs?

In comparison, for estimating purposes Florida DOT now uses a nominal construction cost of $8.2 million per mile of four-lane Interstate with the minimum shoulder widths of four feet on the left and 10 feet on the right.

Thanks for posting this.  Over the years, FDOT has maintained a bunch of great spreadsheets online that are useful in getting a ballpark estimate of highway and transit system costs.  But I've been using older FDOT spreadsheets that may be way out-of-date.  I had gotten where I was only using FDOT information to scale up known costs from other sources (using ratios derived from the older spreadsheets).

[J N Winkler]

Actually, rural land has to be pretty valuable before the cost of acquisition starts to be comparable to construction cost.  Each additional 100 feet in corridor width translates to 13 acres per centerline mile, which is only about $66,000 at the US national average cropland value of $5,050 per acre as of 2022.

That number actually seems a bit high.  Do you know if this is property values or land acquisition costs?

Both values quoted come from a single Google search on the phrase {cost per acre prime farmland Kansas} (no braces).  I relied on the search snippets and didn't actually click through the links.  (It didn't surprise me that the average value for Kansas was lower than for the nation at large, since our ag base is mostly wheat, which is considered one of the less intensive crops.)  I don't think land acquisition costs are included.  The relevant links are as follows:

Kansas farm real estate average land value "about" $3000 (actual figure is $2,630) per acre

US national average cropland value is $5,050 per acre

In comparison, for estimating purposes Florida DOT now uses a nominal construction cost of $8.2 million per mile of four-lane Interstate with the minimum shoulder widths of four feet on the left and 10 feet on the right.

Thanks for posting this.  Over the years, FDOT has maintained a bunch of great spreadsheets online that are useful in getting a ballpark estimate of highway and transit system costs.  But I've been using older FDOT spreadsheets that may be way out-of-date.  I had gotten where I was only using FDOT information to scale up known costs from other sources (using ratios derived from the older spreadsheets).

You are welcome.  I only skimmed that page, but I had the impression the $8.2 million per mile figure is to build out the cross-section to Interstate standards and does not include the added costs of bridges, ramps, etc. for interchanges.

[J N Winkler]

I  vaguely recall hearing about such things myself. Thing is, it's hard for me to reconcile nickel-and-diming minor items like guardrail provision with signing off on 150-200-foot medians and such.

Thinking about this some more, I think part of the difference between the 1960's and now is the incentive structure.  When the Interstates were being built, the feds had a network map and a deadline for system completion.  States had to spend federal Interstate funding on actual Interstates, but otherwise those ten-cent dollars were almost as good as free money.  So keeping a tight rein on design features was one way for BPR/FHWA to curb a natural tendency among engineers in some state DOTs to goldplate.  (This was not universal--some states like North Carolina and Virginia initially did not consider the Interstates relevant to their needs and dragged their feet; the NC highway folks felt they were detrimental to their farm-to-market program, while VDOT/its predecessor agency fought against developing the US 11 corridor to full Interstate standards as I-81.)

Now, FHWA and the state DOTs are dealing with a mature network, no deadline pressure to finish the Interstates, and significant funding constraints.  Within this framework, extra federal money spent on Project A means less to spend on Project B, so the incentive is more to spread the jam as wide as possible while ensuring conformity with standards.

[Dirt Roads]

...I had the impression the $8.2 million per mile figure is to build out the cross-section to Interstate standards and does not include the added costs of bridges, ramps, etc. for interchanges.

That is correct.  There are plenty of other spreadsheets that get filled out to develop the entire cost estimate.  Usually, these templates do include some wiggle room for variations in grade and hydrology.  Nobody wants to calculate any hydrology in the planning phase, but I always found that it was worth the extra effort to develop detailed cross-sections for every transition point and mid-sections in order to get reasonable volume calculations on what those guys call "cut", "fill" and "borrow" (rather than taking the assumptions in these per-mile snapshots). 

Which brings me to something that I've been wondering about on this topic.  Perhaps hydrology (or lack of understanding) was a primary driver in the decision making for right-of-way widths (as well as median width).  Back in those days, most states were still mowing their roadberms with small tractors using short sickle-bars.  I'm sure that perpetual mowing of a 200-foot wide corridor was an intimidating consideration, and could become very slow and labor-intensive if much of the corridor had much more than a 1:12 slope.  From this perspective, the amount of guardrail is also a problem.  Extra-wide medians certainly simplify the hydrology versus tractor-mowing game.

I regularly mow a long 1:4 slopebank that we corrected, and it is still a fairly slow process.  The 1:2 slopebank that NCDOT left us on the other side can only be mowed at a snail's pace (and only when extremely dry).  It is sometimes faster to mow the steep slopebank with a weedeater.  (It's a good thing that I'm from West Virginia, as NCDOT left us with a couple of short sections of 2:1 slopebanks that can only be mowed by weedeater).

[D-Dey65]

I still remember a Newsday article where they referred to the upgrade of NY 27 between NY 454 and Nicoll's Road (Suffolk CR 97) as "The $22 Million Mile."

And since this is my 3300th post, I'm going to celebrate with this;